1. Field of the Invention
The present invention relates to a light emitting device and an organic light emitting display device including the same, and more particularly, to a light emitting device having a decreased number of hetero-junction interfaces through forming some layers using the same material and thus has reduced driving voltage and an organic light emitting display device including the same.
2. Discussion of the Related Art
Image display devices, which display a variety of information on a screen, are a core technology of information and communication and are becoming increasingly thinner, lighter, more portable, and higher in performance. Thus, organic light emitting display devices, which display an image by controlling light emission of an organic emission layer (EML), have received attention as a flat panel display device that may address problems in terms of weight and volume which occur in cathode ray tubes (CRTs). Such organic light emitting display devices do not require separate light sources and are considered a competitive application for compact device fabrication and clear display of colors.
In this regard, organic light emitting display devices are self-emissive devices including a thin EML between electrodes and can be fabricated as a thin film with a thickness similar to that of paper. In particular, an organic light emitting diode includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), an EML, an electron injection layer (EIL), an electron transport layer (ETL), and a cathode.
As such, an organic light emitting display device has a single stack structure. In addition, organic light emitting display devices having a multi-stack structure including a plurality of stacks have been developed.
Such organic light emitting display devices having a multi-stack structure include an anode, a cathode, and a first stack, a charge generation layer, and a second stack that are sequentially stacked between the anode and the cathode.
In this regard, the first stack includes a HTL, an EML, and an ETL that are formed on the anode, and the second stack includes a HTL, an EML, and an ETL.
The charge generation layer is disposed between the first and second stacks to control charge balance of the first and second stacks and includes an n-type charge generation layer and a p-type charge generation layer.
As illustrated in FIG. 1, such organic light emitting display devices having a multi-stack structure have higher driving voltages than those of organic light emitting display devices having a single stack structure and, accordingly, power consumption is increased. FIG. 1 is a graph showing comparison results between driving voltages of organic light emitting display devices respectively having a single stack structure and a multi-stack structure. In FIG. 1, a first graph 20 shows the driving voltage of an organic light emitting device having a single stack structure, and a second graph 22 shows the driving voltage of an organic light emitting device having a structure including first and second stacks. As illustrated in FIG. 1, the driving voltage shown in the second graph 22 is considerably higher than that shown in the first graph 20.
This is because charge trapping occurs at an interface between hetero-organic materials and thus driving voltage is increased due to the charge trapping. Thus, an organic light emitting device having a multi-stack structure has a greater number of stacked organic materials than that of an organic light emitting device having a single stack structure and, accordingly, has an increasing number of junction interfaces between hetero-organic materials, which results in occurrence of charge trapping and thus increased driving voltage.
Therefore, there is a need to develop an organic light emitting display device having a multi-stack structure that has a decreased number of hetero-junction interfaces.